Treatment of electric lamp envelopes



y 5, 1953 A. J. SHARKEY 2,637,830

TREATMENT OF ELECTRIC LAMP ENVELOPES Filed Feb. 28, 1949 I I I '11: 1111111111 'JJIII 1111!!!! 1.1 11! '11! ull'l llf'hllil lll 'lll'lllllll lllr.l-{lnlil.

INVENTOR.

Arronun Patented May 5, 1953 UNITEB PATENT OFFICE TREATMENT OF ELECTRIC LAMP ENVELOPES Application February 28, 1949, Serial No. 78,854

Claims. 1

This invention relates to electric gaseous discharge devices and more particularly to those which contain mercury therein.

An object of this invention is to provide means whereby the decrease in light output of electric gaseous discharge devices during life may be retarded.

Another object is to provide means for reducing the discoloration which develops on the walls of electric gaseous discharge devices during life.

Further objects, advantages and features will be apparent from the following description thereof when read in conjunction with the accompanying drawing in which the single figure is a side elevational view in section of a. lamp embodying the teaching of my invention.

In the art of manufacturing electric gaseous discharge devices, such as fluorescent and germicidal lamps, for example, it has been known that the light output of these devices drops oil? during life. It has also been noted that the Walls of the envelope of these devices becomes discolored during life and that this discoloration increases as the life or length of time during which the device has been used increases. found that the decrease in light output and the development of discoloration may be substantially retarded by providing the inner wall of the envelope with a thin surface coating of an oxide of antimony.

A specific application of the teaching of my invention is the treatment of the glass envelope of a -watt T-8 germicidal lamp designed for operation in refrigerators. In the figure, the lamp comprises an elongated tubular glass envelope I, having filamentary electrodes 2 sealed therein at the extremities thereof. These filamentary electrodes are provided with a coating of electron-emissive material, usually an oxide of one or more of the alkaline earth metals. The lamp contains a small amount of mercury 3 such as about mg. for example, and a filling of inert gas, such as argon, at about 3 mm. pres sure. The inner wall of the envelope I is provided with a thin surface coating 4 of an oxide of antimony.

In accordance with my invention, the inner wall of the tubular glass envelope l is coated with a suspension containing an oxide of antimony. This suspension comprises a binder, a vehicle in which the binder is soluble, and the antimony. When ethyl cellulose is used as the binder, xylol may be employed as the vehicle. If nitrocellulose is used as the binder, butyl acetate or amyl acetate may be employed as the I have 2 vehicle. However other binders and suitable solvents therefor may be employed without departing from the spirit of my invention.

In preparing the suspension I add a small amount of powdered oxide of antimony to a mixture of ethyl cellulose and xylol. The inner wall oi the glass envelope is then coated with this suspension and the coated envelope is heated to a temperature high enough to break down the ethyl cellulose, i. e. about 450 C. to about 550 C. thus leaving a. thin surface layer of an oxide of antimony on the wall of the envelope. The lamp is then processed in the conventional manner well known to those skilled in the art. The

" data below shows the marked improvement in retarding the decrease in light output during life of l5-watt T-8 germicidal lamps. In this test the control represents several lamps which were not provided with a surface layer of antimony on the inner wall of the lamp en- Table Hours of Operation 0 112 295 507 1 mg. SbzOa 64. 2 4. 0 46. 0 Control 100 58. 6 41. 0 27. 6

This test clearly shows that when the inner wall of the lamp envelope is provided with a thin surface layer rich in antimony, the decrease in light output during life is retarded substantially. The discoloration of the envelope wall in the case of the lamps having the oxide of antimony coating was slower in developing and less intense than the discoloration of the controls.

Although the test illustrated in the table was made with germicidal lamps, similar beneficial effects may be obtained in the case of other electric gaseous discharge devices, such as fluorescent lamps for example. In the case of fluorescent lamps, the inner wall of the tubular glass envelope may be treated in, the manner described above, before the coating cf fluorescent material is applied.

The lamps used in the test of the table were 15 watt T-8 lamps and the lamp envelope was coated with a suspension containing 1 mg. of SbzOs. However, between 0.5 mg. to 5 mgs. may be added. If less than 0.5 mg. is added, there doesnt appear to be enough antimony present to effect any substantial improvement. If more than 5 mgs. of SbzOa are added, yellow bands develop on the wall of the envelope.

In the specific example above, 1 mg. of SbzOs was added to a suspension with which the envelope of a 15 watt T-8 lamp was coated. This is equal to about .02 mg. per square inch. 00rrespondingly, conversion of the 0.5 mg. to 5 mgs. range described above results in a range of between .01 mg. per square inch to 0.1 mg. per square inch. Since about 70% of the Sb203 is lost during baking when the binder is burned off, the amount of SbzOs left in the finished lamp is between .003 mg. per sq. in. to .03 mg. per sq. in.

Although I have used antimony trioxide, any oxide of antimony, such an antimony pentoxide for example, may be used.

What I claim is:

1. An electric gaseous discharge device comprising: a sealed, glass, light-transmitting envelope; a filling of inert gas at a pressure of a few millimeters in said envelope; a filling of mercury in said envelope; spaced electrodes contained within said envelope; a coating of an oxide of at least one of the alkaline earth metals on said electrodes; and a single coating on the inner wall of said envelope, said coating consisting essentially of between about .003 mg. to about .03 mg. per square inch of an oxide of antimony.

2. An electric gaseous discharge device comprising: a sealed, glass, light-transmitting envelope; a filling of inert gas at a pressure of a few millimeters in said envelope; a filling of mercury in said envelope; spaced electrodes contained within said envelope; a coating of an oxide of at least one of the alkaline earth metals on said electrodes; and a single coating on the inner wall of said envelope, said coating consisting essentially of about .006 mg. per square inch of an oxide of antimony.

3. An electric gaseous discharge device comprising: a sealed, glass, light-transmitting envelope; a filling of inert gas at a pressure of a few millimeters in said envelope; a filling of mercury in said envelope; spaced electrodes contained within said envelope; a coating of an oxide of at least one of the alkaline earth metals on said electrodes; and a single coating on the inner wall of said envelope, said coating consisting essentially of between about .003 mg. to about .03 mg. per square inch of 813203.

4. An electric gaseous discharge device comprising: a sealed, glass, light-transmitting envelope; a filling of inert gas at a pressure of a few millimeters in said envelope; a filling of mercury in said envelope; spaced electrodes contained within said envelope; a coating of an oxide of at least one of the alkaline earth metals on said electrodes; and a single coating on the inner wall of said envelope, said coating consisting essentially of about .006 mg. per square inch of 811203.

5. An ultra violet electric gaseous discharge lamp comprising an elongated tubular envelope, said envelope having a portion of glass which is transmissive of ultra violet radiations, a filling of inert gas at a pressure of a few millimeters sealed in said envelope; a small quantity of mercury also sealed in said envelope, spaced electrodes sealed into the ends of said envelope, a coating of an oxide of at least one of the alkaline earth metals on said electrodes, and a single coating on th inner wall of said envelope, said coating being relatively thin and consisting of antimony trioxide.

ARTHUR J. SHARKEY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,998,371 Koch Apr. 16, 1935 2,097,275 Fischer Oct. 26, 1937 2,177,691 Dawihl Oct. 31, 1939 2,182,732 Meyer Dec. 5, 1939 2344,081 Claude Mar. 14, 1944 2,496,065 OHearn Jan. 31, 1950 

1. AN ELECTRIC GASEOUS DISCHARGE DEVICE COMPRISING: A SEALED, GLASS, LIGHT-TRANSMITTING ENVELOPE; A FILLING OF INERT GAS AT A PRESSURE OF A FEW MILLIMETERS IN SAID ENVELOPE; A FILLING OF MERCURY IN SAID ENVELOPE; SPACED ELECTRODES CONTAINED WITHIN SAID ENVELOPE; A COATING OF AN OXIDE OF AT LEAST ONE OF THE ALKALINE EARTH METALS ON SAID ELECTRODES; AND A SINGLE COATING ON THE INNER WALL OF SAID ENVELOPE, SAID COATING CONSISTING ESSENTIALLY OF BETWEEN ABOUT .003 MG. TO ABOUT .03 MG. PER SQUARE INCH OF AN OXIDE OF ANTIMONY. 